"Seashore is an open source image editor for Cocoa. It features gradients, textures and anti-aliasing for both text and brush strokes. It supports multiple layers and alpha channel editing. It is based around the GIMP's technology and uses the same native file format."

When they say "alpha channel", it means transparency.

koltz

The most easily way is to take viewer (ifranview for exampe)
transparent as you want and do printscreen

OS Master

I use Paint.Net. It automatically has a background layer but you can delete it (have to make another layer first), and you have a transparent image!